A Digital Soyuz

Russian crew spacecraft replaces its computer and analog parts for a new mission

By James Oberg

Posted 28 Sep 2010 | 14:21 GMT

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Illustration: Russian Space Agency/James Oberg

28 September 2010—For almost 40 years, the Soyuz series of spacecraft has carried cosmonauts into orbit and back safely, if not always comfortably. The workhorse human transport vehicle has undergone a series of upgrades during that period, and it is now about to undergo its latest—and probably final—revision. At long last, Soyuz is all digital.

The next Soyuz launch, scheduled for 8 October, marks the culmination of a series of overhauls that will allow the launch rate of Soyuz crafts to double—a rate needed to maintain a crew of six aboard the International Space Station (ISS) in the absence of the retiring U.S. space shuttle fleet.

Although the craft’s outward appearance will not change, Nikolai Bryukhanov, deputy general designer for S.P. Korolev Rocket & Space Corp. Energia, told reporters at the Baikonur Cosmodrome, in Kazakhstan, that "the new Soyuz…will be more convenient for testing." And it’s the rapid testing that will allow for the more frequent launches required. The previous Soyuz contained five incompatible analog processors for monitoring different spacecraft systems—each with its own telemetry transmitters—plus the main guidance computer, the venerable Argon flight computer, a ruggedly reliable system that has been in use for more than 30 years.

The analog units will all be replaced by a single new digital device called MBITS (the Russian acronym for "small-sized onboard informational telemetry system"), but no performance specs have been released. MBITS promises to make transmission of spacecraft parameters much more efficient, resulting in significant time savings in prelaunch checkout and a major improvement in overseeing the vehicles in flight.

Illustration: Russian Space Agency/James Oberg

Click on the image for the full illustration view.

In use since 1974, the triply redundant Argon-16 had 2 kilobytes of RAM and 16 kB of ROM and ran at 200 000 operations per second. Its replacement is a much lighter CPU called the TsVM-101 (for "central computing machine"). The TsVM-101 is a much smaller, faster unit capable of 6 million operations per second but with a very modest memory—2 megabytes of RAM, 2 MB of ROM—befitting its modest mission requirements.

Soyuz vehicles have never required computational capability anywhere near the levels of NASA’s space shuttles, or even the Apollo lunar vehicles of the 1960s and 1970s. The autopilot performs only routine functions plus special but rather straightforward tasks, such as rendezvous, docking, deorbit, and atmospheric entry. The autopilot conducts routine monitoring in flight and formats data about the ship’s status for transmission to Earth. The new hardware will also replace many avionics components manufactured at facilities in former Soviet states now independent of Russia. In all, the upgrade replaces 36 old devices with 19 new ones that are lighter, perform better, and consume less power. Most of this hardware has already been flight-tested on unmanned Progress space freighters during the past two years.

Despite all the upgrades, "the flight crews will see almost no change," Bryukhanov said, "as the new spaceship will have a familiar interface that cosmonauts have been trained to operate." However, some changes have already been made for the crew’s convenience: Color displays replace monochrome ones, and control panels have been more ergonomically arranged. (The modernization will also more than double the cargo capacity of the cramped vehicle, from 50 kilograms to 120 kg, giving more flexibility to deliver repair tools and parts to the ISS in the absence of the space shuttle.)

Taken together with the new CPU and status indicators, these changes will now allow the Soyuz to be flown by a single professional pilot, accompanied by two crew members who need only minimal training on Soyuz systems and thus will be better prepared for their specialized in-orbit activities. The previous design required two fully trained crew members, with the third seat available for a research specialist with limited Soyuz flight duties.

However small the changes may seem to cosmonauts, officials have approached the upgrade with extreme care. Crew members have already used the new CPU on a series of automated dockings of the Progress supply ships over the past two years. And Russia’s most experienced cosmonaut flight engineer, Aleksandr Kaleri, will command this first manned mission. In a highly unusual move, reflecting the presumed difficulty of the flight, a special backup team of veteran cosmonaut commanders was also assigned to the launch.

Two of the old spacecraft models remain in inventory. "New spaceships may have certain problems, and we will need time to resolve them," Bryukhanov said. "Thus, we will launch an old spaceship after the modernized Soyuz. That will give us time for an analysis."

As an additional precaution, the Russian Space Agency has shipped an old-model Soyuz (TMA-20), originally slated for launch in December, to Baikonur and is readying it as a backup vehicle for the October launch of the digital Soyuz.

The Soyuz overhaul is part of a broader process to upgrade Russian spacecraft avionics. In addition to its installation in the Soyuz and the Progress, the TsVM-101 computer will also be integrated into the Kondor and Arkon-2 series of unmanned satellites. A similar computer is being introduced in the fourth stage of the Proton, Russia’s biggest and most commercially successful rocket. And the long-delayed Glonass NavSat constellation will soon include Glonass-K payloads with greatly extended service lifetimes and modernized control computers.

About the Author

James Oberg worked as an aerospace engineer at NASA for 22 years. He switched to journalism in the late 1990s and now makes his living reporting on space for such outlets as Popular Science, NBC News, and of course, IEEE Spectrum. In August 2010, he reported on how the repair of the International Space Station’s cooling system was a test of NASA’s ability to keep the station running.